What's the Justice League sequel look like?
Unlike Batman v Superman, the first Justice League movie doesn't directly point to its next installment. The next movies that actually have dates attached to them (for now) are Aquaman, arriving December 21, 2018, Shazam!, starring starring Dwayne Johnson and Zachary Levi and due in April 2019, Wonder Woman 2 later in 2019, and the standalone Cyborg and Green Lantern Corps in 2020.
There are a bunch of other DC movies in development, either continually rumored or reworking their original premises to fit the DCEU, including a solo Batman movie, Flashpoint (i.e. the Flash movie), a movie based on the Batman character Nightwing from The LEGO Batman Movie director Chris McKay, and a Batgirl movie from director Joss Whedon. None of the films are locked into a release date. Just where the Injustice League (likely) and/or a Flash and Superman race (unlikely) could become consequential is a guessing game. Aquaman will probably be isolated with director James Wan steering clear of Justice League's troubled production, nobody really knows anything about Shazam!, so... how does Justice League prep us for Wonder Woman 2? With Patty Jenkins and Gal Godot returning for the sequel, another period piece that Jenkins hinted at during the press tour for the first film, all signs also point to autonomy for the follow-up. That means almost zero connection to the battle with Steppenwolf.